MC68HC05RC8 Datasheet, PDF (76/122 Pages) Freescale Semiconductor, Inc – General Release Specification

Freescale Semiconductor, Inc.
Carrier Modulator Transmitter (CMT)
9.5.1 Time Mode
When the modulator operates in time mode, the modulation mark and
space periods consist of zero or an integer number of f_osc ÷ 8 clocks
(= 250 kHz @ 2 MHz osc). This provides a modulator resolution of 4 µs
and a maximum mark and space periods of about 16 ms (each).
However, to prevent carrier glitches which could affect carrier spectral
purity, the modulator control gate and carrier clock are synchronized.
The carrier signal is activated when the modulator gate opens. The
modulator gate can only close when the carrier signal is low (the output
logic level during space periods is low). If the carrier generator is in
baseband mode (BASE bit in MCSR is high), the modulator output will
be at a logic one for the duration of the mark period and at a logic zero
for the duration of a space period. See Figure 9-8.
The mark and space time equations are:
tmark = ⁽---M-----B-----U----F-f--o-F--s---+-c----1----⁾---^×-----8-- sec s
tspace = ^{S-----B----U-f--o--F-s---F-c----×}-----8--sec s
Setting the DIV2 bit in the MCSR will double mark and space times.
General Release Specification
MC68HC05RC16 — Rev. 3.0
Carrier Modulator Transmitter (CMT)
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